The present invention relates to corona discharge members used for depositing a charge on an adjacent surface, and more particularly, relates to corona discharge electrodes and a method of making corona discharge electrodes.
In the electrophotographic reproducing arts, it is necessary to deposit a uniform electrostatic charge on an imaging surface, which charge is subsequently selectively dissipated by exposure to an information containing optical image to form an electrostatic latent image. The electrostatic latent image may then be developed and the developed image transferred to a support surface to form a final copy of the original document.
In addition to precharging the imaging surface of a xerographic system prior to exposure, corona devices are used to perform a variety of other functions in the xerographic process. For example, corona devices aid in the transfer of an electrostatic toner image for a reusable photoreceptor to a transfer member, the tacking and de-tacking of paper to the imaging member, the conditioning of the imaging surface prior to, during and after the deposition of toner thereon to improve the quality of the xerographic copy produced thereby, the cleaning of certain photoconductive members and the like. Both direct current and alternating current type corona devices are used to perform many of the above functions.
One type of improved corona charging device is disclosed in U.S. Pat. No. 4,086,650 wherein the corona discharge member comprises a thin wire, coated at least in the discharge area with a dielectric material. In a preferred embodiment, this corona discharge member is positioned above a charge collecting surface carried on a conductive substrate held at a reference potential, and it is provided with means for coupling a corona generating voltage intermediate the conductive substrate and the wire of the corona discharge member. A conductive shield adjacent the wire and a first biasing means for holding the shield at a potential different from the reference potential is also provided in the preferred embodiment.
Many of the prior art problems conventionally associated with charging devices have been overcome by the dielectric-coated thin wire of U.S. Pat. No. 4,086,650. However, improved uniformity in currents and increased life of the dielectric-coated wire are desirable.